This invention relates in general to air vehicles and, more specifically to unmanned air vehicles capable of vertical take-off, landing, hovering and high speed horizontal flight.
Conventional heavier-than-air aircraft utilize propellers or gas turbines to drive the aircraft through the air at a sufficient velocity that lift generated by a large wing is sufficient to maintain the aircraft in flight. While providing very high speeds from point to point over the earth, these aircraft require long runways for landing and take-off. A number of small, unmanned aircraft have been designed for reconnaissance and surveillance purposes, carrying various sensors and in some cases light weapons, such as in the case of small, homing, anti-radiation aircraft intended to detect and destroy radar transmitters. Generally, these unmanned aircraft use propellers due to the greater range when compared to jet engines. These aircraft require long runways for take-off and landing, or in some cases large catapult systems for take-off and large nets for retrieval, making them difficult to operate from ships or confined areas.
Helicopters have come into widespread use for carrying passengers or cargo over relatively short distances. The vertical landing and take-off characteristics make them especially useful on shipboard and in confined areas, such as roof tops. Helicopters are little used where long endurance or long distance flights are required because of their relatively high fuel consumption and low cross country speed. Attempts have been made to develop small helicopters for reconnaissance and surveillance purposes. Where large helicopters generally use an extended tail rotor to counteract rotor blade torque on the fuselage, small helicopter tend to use pairs of counter rotating rotor blade sets, increasing system complexity. Launch and recovery of small helicopters tends to be dangerous where the blades are rotating in a confined area. Further, miniature helicopters have very low cross country speed and relatively high fuel consumption so that they cannot cover large areas.
A compact, but pilot-carrying, helicopter is described by Velton in U.S. Pat. No. 3,584,810. The pilot rides between two vertically spaced, counter rotating, rotors positioned in narrow ducts, one above and one below the pilot. This is a complex and heavy arrangement, which if scaled down would not be effective for surveillance purposes, since a sensor between the rotors in place of the pilot would be effectively masked by the rotating blades except over a narrow horizontal band. Further, this helicopter would also have the speed and range limitations common to helicopters.
Aircraft have been designed that can take-off vertically, transition to horizontal flight, then transition back to vertical flight for landing. Some are "tail sitters" with the aircraft fuselage vertical on the ground. Others have pivoting engines or tilting wings to move propellers from a horizontal plane for take-off to a vertical plane for flight. Still others have elaborate duct systems moveable to direct jet exhaust vertically or horizontally. The mechanisms for transition between vertical and horizontal flight in these aircraft tend to be very heavy and complex. These aircraft generally have low payload capacities, often requiring horizontal take-off runs to achieve flight with the necessary fuel aboard to provide reasonable flight endurance.
Thus, there is a continuing need for light weight, simple and safe unmanned air vehicles for reconnaissance, surveillance, weapon delivery and the like that can take-off from and land vertically in confined areas while providing sufficient horizontal speed to furnish the necessary flight endurance for many surveillance purposes. The ability to carry a variety of sensors in a manner permitting sensing over a wide area is also needed.